The volcano's frequent large eruptions have covered much of Iceland with tephra and these layers can be used to date eruptions of Iceland's other volcanos. 10% of the tephra created in Iceland in the last thousand years has come from Hekla, amounting to 5 km3. The volcano has produced one of the largest volumes of lava of any in the world in the last millennium, around 8 km3. [link to en.wikipedia.org]